The southwest monsoon reached sub-Himalayan West Bengal on Friday, covering most parts of the region, nearly a week ahead of schedule, the Met Department said.

The southwest monsoon normally reaches northern West Bengal on June 5 and the southern part of the state around June 9.

The faster movement of the southwest monsoon into the region could have been caused by the combined effect of cyclone Remal, bringing the southwesterly wind to the coasts from the Bay of Bengal, and thereafter the monsoon's movement was attracted by a trough existing over northern West Bengal, weather officials said.

The weather office forecast widespread rain in the sub-Himalayan districts of Cooch Behar, Jalpaiguri, Alipurduar, Kalimpong and Darjeeling, with the possibility of heavy downpours in one or two places, over the next five days.

The places that recorded significant rainfall in 24 hours till 8.30 am on Friday in northern Bengal are Alipurduar (45 mm), Jalpaiguri (43 mm) and Coochbehar (28 mm), it said.

The Met Department also forecast thunderstorms with lightning and gusty wind in the southern Bengal districts, including Calcutta, during the next three days.

Calcutta recorded 65 mm rainfall, bringing night temperature down to 23.7 degree Celsius from nearly 30 degrees a day earlier, the Met said.